2 * hazard-pointer.c: Hazard pointer related code.
4 * (C) Copyright 2011 Novell, Inc
5 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
12 #include <mono/utils/hazard-pointer.h>
13 #include <mono/utils/mono-membar.h>
14 #include <mono/utils/mono-memory-model.h>
15 #include <mono/utils/monobitset.h>
16 #include <mono/utils/lock-free-array-queue.h>
17 #include <mono/utils/atomic.h>
18 #include <mono/utils/mono-os-mutex.h>
19 #ifdef SGEN_WITHOUT_MONO
20 #include <mono/sgen/sgen-gc.h>
21 #include <mono/sgen/sgen-client.h>
23 #include <mono/utils/mono-mmap.h>
24 #include <mono/utils/mono-threads.h>
25 #include <mono/utils/mono-counters.h>
26 #include <mono/io-layer/io-layer.h>
31 MonoHazardousFreeFunc free_func;
32 HazardFreeLocking locking;
35 /* The hazard table */
37 #define HAZARD_TABLE_MAX_SIZE 256
38 #define HAZARD_TABLE_OVERFLOW 4
40 #define HAZARD_TABLE_MAX_SIZE 16384 /* There cannot be more threads than this number. */
41 #define HAZARD_TABLE_OVERFLOW 64
44 static volatile int hazard_table_size = 0;
45 static MonoThreadHazardPointers * volatile hazard_table = NULL;
46 static MonoHazardFreeQueueSizeCallback queue_size_cb;
49 * Each entry is either 0 or 1, indicating whether that overflow small
52 static volatile gint32 overflow_busy [HAZARD_TABLE_OVERFLOW];
54 /* The table where we keep pointers to blocks to be freed but that
55 have to wait because they're guarded by a hazard pointer. */
56 static MonoLockFreeArrayQueue delayed_free_queue = MONO_LOCK_FREE_ARRAY_QUEUE_INIT (sizeof (DelayedFreeItem));
58 /* The table for small ID assignment */
59 static mono_mutex_t small_id_mutex;
60 static int small_id_next;
61 static int highest_small_id = -1;
62 static MonoBitSet *small_id_table;
63 static int hazardous_pointer_count;
66 * Allocate a small thread id.
68 * FIXME: The biggest part of this function is very similar to
69 * domain_id_alloc() in domain.c and should be merged.
72 mono_thread_small_id_alloc (void)
76 mono_os_mutex_lock (&small_id_mutex);
79 small_id_table = mono_bitset_new (1, 0);
81 id = mono_bitset_find_first_unset (small_id_table, small_id_next - 1);
83 id = mono_bitset_find_first_unset (small_id_table, -1);
86 MonoBitSet *new_table;
87 if (small_id_table->size * 2 >= (1 << 16))
88 g_assert_not_reached ();
89 new_table = mono_bitset_clone (small_id_table, small_id_table->size * 2);
90 id = mono_bitset_find_first_unset (new_table, small_id_table->size - 1);
92 mono_bitset_free (small_id_table);
93 small_id_table = new_table;
96 g_assert (!mono_bitset_test_fast (small_id_table, id));
97 mono_bitset_set_fast (small_id_table, id);
100 if (small_id_next >= small_id_table->size)
103 g_assert (id < HAZARD_TABLE_MAX_SIZE);
104 if (id >= hazard_table_size) {
105 #if MONO_SMALL_CONFIG
106 hazard_table = g_malloc0 (sizeof (MonoThreadHazardPointers) * HAZARD_TABLE_MAX_SIZE);
107 hazard_table_size = HAZARD_TABLE_MAX_SIZE;
110 int pagesize = mono_pagesize ();
111 int num_pages = (hazard_table_size * sizeof (MonoThreadHazardPointers) + pagesize - 1) / pagesize;
113 if (hazard_table == NULL) {
114 hazard_table = (MonoThreadHazardPointers *volatile) mono_valloc (NULL,
115 sizeof (MonoThreadHazardPointers) * HAZARD_TABLE_MAX_SIZE,
119 g_assert (hazard_table != NULL);
120 page_addr = (guint8*)hazard_table + num_pages * pagesize;
122 mono_mprotect (page_addr, pagesize, MONO_MMAP_READ | MONO_MMAP_WRITE);
125 hazard_table_size = num_pages * pagesize / sizeof (MonoThreadHazardPointers);
128 g_assert (id < hazard_table_size);
129 for (i = 0; i < HAZARD_POINTER_COUNT; ++i)
130 hazard_table [id].hazard_pointers [i] = NULL;
133 if (id > highest_small_id) {
134 highest_small_id = id;
135 mono_memory_write_barrier ();
138 mono_os_mutex_unlock (&small_id_mutex);
144 mono_thread_small_id_free (int id)
146 /* MonoBitSet operations are not atomic. */
147 mono_os_mutex_lock (&small_id_mutex);
149 g_assert (id >= 0 && id < small_id_table->size);
150 g_assert (mono_bitset_test_fast (small_id_table, id));
151 mono_bitset_clear_fast (small_id_table, id);
153 mono_os_mutex_unlock (&small_id_mutex);
157 is_pointer_hazardous (gpointer p)
160 int highest = highest_small_id;
162 g_assert (highest < hazard_table_size);
164 for (i = 0; i <= highest; ++i) {
165 for (j = 0; j < HAZARD_POINTER_COUNT; ++j) {
166 if (hazard_table [i].hazard_pointers [j] == p)
175 MonoThreadHazardPointers*
176 mono_hazard_pointer_get (void)
178 int small_id = mono_thread_info_get_small_id ();
181 static MonoThreadHazardPointers emerg_hazard_table;
182 g_warning ("Thread %p may have been prematurely finalized", (gpointer) (gsize) mono_native_thread_id_get ());
183 return &emerg_hazard_table;
186 return &hazard_table [small_id];
189 /* Can be called with hp==NULL, in which case it acts as an ordinary
190 pointer fetch. It's used that way indirectly from
191 mono_jit_info_table_add(), which doesn't have to care about hazards
192 because it holds the respective domain lock. */
194 get_hazardous_pointer (gpointer volatile *pp, MonoThreadHazardPointers *hp, int hazard_index)
199 /* Get the pointer */
201 /* If we don't have hazard pointers just return the
205 /* Make it hazardous */
206 mono_hazard_pointer_set (hp, hazard_index, p);
207 /* Check that it's still the same. If not, try
210 mono_hazard_pointer_clear (hp, hazard_index);
220 mono_hazard_pointer_save_for_signal_handler (void)
223 MonoThreadHazardPointers *hp = mono_hazard_pointer_get ();
224 MonoThreadHazardPointers *hp_overflow;
226 for (i = 0; i < HAZARD_POINTER_COUNT; ++i)
227 if (hp->hazard_pointers [i])
232 for (small_id = 0; small_id < HAZARD_TABLE_OVERFLOW; ++small_id) {
233 if (!overflow_busy [small_id])
238 * If this assert fails we don't have enough overflow slots.
239 * We should contemplate adding them dynamically. If we can
240 * make mono_thread_small_id_alloc() lock-free we can just
241 * allocate them on-demand.
243 g_assert (small_id < HAZARD_TABLE_OVERFLOW);
245 if (InterlockedCompareExchange (&overflow_busy [small_id], 1, 0) != 0)
248 hp_overflow = &hazard_table [small_id];
250 for (i = 0; i < HAZARD_POINTER_COUNT; ++i)
251 g_assert (!hp_overflow->hazard_pointers [i]);
254 mono_memory_write_barrier ();
256 memset (hp, 0, sizeof (MonoThreadHazardPointers));
262 mono_hazard_pointer_restore_for_signal_handler (int small_id)
264 MonoThreadHazardPointers *hp = mono_hazard_pointer_get ();
265 MonoThreadHazardPointers *hp_overflow;
271 g_assert (small_id < HAZARD_TABLE_OVERFLOW);
272 g_assert (overflow_busy [small_id]);
274 for (i = 0; i < HAZARD_POINTER_COUNT; ++i)
275 g_assert (!hp->hazard_pointers [i]);
277 hp_overflow = &hazard_table [small_id];
281 mono_memory_write_barrier ();
283 memset (hp_overflow, 0, sizeof (MonoThreadHazardPointers));
285 mono_memory_write_barrier ();
287 overflow_busy [small_id] = 0;
291 try_free_delayed_free_item (HazardFreeContext context)
293 DelayedFreeItem item;
294 gboolean popped = mono_lock_free_array_queue_pop (&delayed_free_queue, &item);
299 if ((context == HAZARD_FREE_ASYNC_CTX && item.locking == HAZARD_FREE_MAY_LOCK) ||
300 (is_pointer_hazardous (item.p))) {
301 mono_lock_free_array_queue_push (&delayed_free_queue, &item);
305 item.free_func (item.p);
311 * mono_thread_hazardous_try_free:
312 * @p: the pointer to free
313 * @free_func: the function that can free the pointer
315 * If @p is not a hazardous pointer it will be immediately freed by calling @free_func.
316 * Otherwise it will be queued for later.
318 * Use this function if @free_func can ALWAYS be called in the context where this function is being called.
320 * This function doesn't pump the free queue so try to accommodate a call at an appropriate time.
321 * See mono_thread_hazardous_try_free_some for when it's appropriate.
323 * Return: TRUE if @p was free or FALSE if it was queued.
326 mono_thread_hazardous_try_free (gpointer p, MonoHazardousFreeFunc free_func)
328 if (!is_pointer_hazardous (p)) {
332 mono_thread_hazardous_queue_free (p, free_func);
338 * mono_thread_hazardous_queue_free:
339 * @p: the pointer to free
340 * @free_func: the function that can free the pointer
342 * Queue @p to be freed later. @p will be freed once the hazard free queue is pumped.
344 * This function doesn't pump the free queue so try to accommodate a call at an appropriate time.
345 * See mono_thread_hazardous_try_free_some for when it's appropriate.
349 mono_thread_hazardous_queue_free (gpointer p, MonoHazardousFreeFunc free_func)
351 DelayedFreeItem item = { p, free_func, HAZARD_FREE_MAY_LOCK };
353 InterlockedIncrement (&hazardous_pointer_count);
355 mono_lock_free_array_queue_push (&delayed_free_queue, &item);
357 guint32 queue_size = delayed_free_queue.num_used_entries;
358 if (queue_size && queue_size_cb)
359 queue_size_cb (queue_size);
364 mono_hazard_pointer_install_free_queue_size_callback (MonoHazardFreeQueueSizeCallback cb)
370 mono_thread_hazardous_try_free_all (void)
372 while (try_free_delayed_free_item (HAZARD_FREE_SAFE_CTX))
377 mono_thread_hazardous_try_free_some (void)
380 for (i = 0; i < 10; ++i)
381 try_free_delayed_free_item (HAZARD_FREE_SAFE_CTX);
385 mono_thread_smr_init (void)
389 mono_os_mutex_init_recursive(&small_id_mutex);
390 mono_counters_register ("Hazardous pointers", MONO_COUNTER_JIT | MONO_COUNTER_INT, &hazardous_pointer_count);
392 for (i = 0; i < HAZARD_TABLE_OVERFLOW; ++i) {
393 int small_id = mono_thread_small_id_alloc ();
394 g_assert (small_id == i);
399 mono_thread_smr_cleanup (void)
401 mono_thread_hazardous_try_free_all ();
403 mono_lock_free_array_queue_cleanup (&delayed_free_queue);
405 /*FIXME, can't we release the small id table here?*/